System for controlling turbocharger compressor surge

Abstract

A system for controlling turbocharger compressor surge includes a turbocharger compressor fluidly coupled to an engine intake manifold, an exhaust gas recirculation (EGR) valve disposed in-line with an EGR conduit fluidly coupled between the engine intake and exhaust manifolds, means for determining a mass flow parameter, a speed sensor producing a speed signal indicative of turbocharger speed, and a control computer configured to determine a mass flow rate surge value, corresponding to a fresh air mass flow rate above which turbocharger compressor surge is avoided, as a function of the speed signal, and to limit the EGR valve position and VGT position as a function of the mass flow parameter and the mass flow rate surge value to maintain exhaust gas flow through the EGR valve at a flow rate below which turbocharger compressor surge is avoided.

1. System for controlling turbocharger compressor surge, comprising:
 an internal combustion engine having intake and exhaust manifolds; 
 a turbocharger including a compressor having an inlet fluidly coupled to ambient and an outlet fluidly coupled to said intake manifold; 
 an exhaust gas recirculation (EGR) valve disposed in-line with an EGR conduit fluidly coupled between said intake and exhaust manifolds, said EGR valve responsive to an EGR valve control signal to control exhaust gas flow therethrough; 
 means for determining a mass flow parameter corresponding to a mass flow rate of fresh air supplied to said intake manifold; 
 a speed sensor producing a speed signal indicative of turbocharger speed; and 
 a control computer configured to determine a mass flow rate surge value, corresponding to a fresh air mass flow rate above which turbocharger compressor surge is avoided, as a function of said speed signal, said control computer limiting said EGR valve control signal as a function of said mass flow parameter and said mass flow rate surge value to maintain exhaust gas flow through said EGR valve at a flow rate below which said turbocharger compressor surge is avoided. 
 
   
   
     2. The system of  claim 1  further including a compressor inlet temperature sensor producing a compressor inlet temperature signal indicative of turbocharger compressor inlet temperature,
 and wherein the control computer is configured to determine the said mass flow surge value further as a function of said compressor inlet temperature signal. 
 
   
   
     3. The system of  claim 1  further including a compressor inlet pressure sensor producing a compressor inlet pressure signal indicative of turbocharger compressor inlet pressure,
 and wherein the control computer is configured to determine the said mass flow surge value further as a function of said compressor inlet pressure signal. 
 
   
   
     4. The system of  claim 1  wherein said mass flow parameter corresponds to a mass flow rate of fresh air supplied by said compressor to said intake manifold;
 and wherein said control computer is configured to determine a flow ratio as a ratio of said mass flow rate surge value and said mass flow rate of fresh air, said control computer limiting said EGR valve control signal as a function of said flow ratio. 
 
   
   
     5. The system of  claim 4  further including:
 a compressor inlet temperature sensor producing a compressor inlet temperature signal indicative of turbocharger compressor inlet temperature, and 
 a compressor inlet pressure sensor producing a compressor inlet pressure signal indicative of turbocharger compressor inlet pressure, 
 wherein the control computer is configured to determine the mass flow parameter as a ratio of a product of the mass flow rate of fresh air and a square root of the compressor inlet temperature signal and the compressor inlet pressure signal. 
 
   
   
     6. The system of  claim 4  wherein said control computer includes:
 means for producing an EGR fraction command corresponding to a desired fraction of recirculated exhaust gas relative to an air charge supplied to said intake manifold, said air charge being a combination of recirculated exhaust gas and fresh air; 
 means responsive to said EGR fraction command and said flow ratio to produce a limited EGR fraction command corresponding to an EGR fraction below which turbocharger compressor surge is avoided; and 
 means responsive to said limited EGR fraction command to produce said EGR valve control signal. 
 
   
   
     7. The system of  claim 6  wherein said control computer is further configured to determine a mass flow rate surge limit, corresponding to a fresh air mass flow rate greater than said mass flow rate surge value, as a function of said speed signal;
 and wherein said control computer is configured to determine said flow ratio further as a function of said mass flow rate surge limit. 
 
   
   
     8. The system of  claim 7  wherein said control computer is configured to determine a surge limit percentage as a sum of one and a ratio of said mass flow rate surge limit and one hundred;
 and wherein said control computer is configured to compute a mass flow rate limit as a product of said mass flow rate surge value and said surge limit percentage, and to determine said flow ratio as a ratio of said mass flow rate limit and of said mass flow of fresh air. 
 
   
   
     9. The system of  claim 4  wherein said control computer includes:
 means for producing an EGR fraction command corresponding to a desired fraction of recirculated exhaust gas relative to an air charge supplied to said intake manifold, said air charge being a combination of recirculated exhaust gas and fresh air; 
 means responsive to said EGR fraction command to produce said EGR valve control signal; 
 means for determining a charge flow value corresponding to a mass flow rate of said air charge; and 
 means for limiting said EGR valve control signal as a function of said flow ratio and of said charge flow value to maintain exhaust gas flow through said EGR valve at said flow rate below which said turbocharger compressor surge is avoided. 
 
   
   
     10. The system of  claim 9  wherein said means for limiting said EGR valve control signal includes:
 means for determining a reduction value as a function of said flow ratio and said charge flow value, said reduction value corresponding to an amount of reduction of said exhaust gas flow through said EGR valve required to maintain exhaust gas flow therethrough at said flow rate below which said turbocharger compressor surge is avoided; and 
 means for limiting said EGR valve control signal as a function of said reduction value and said EGR valve control signal only if said flow ratio is greater than or equal to a predefined ration value. 
 
   
   
     11. The system of  claim 9  wherein said control computer is further configured to determine a mass flow rate surge limit, corresponding to a fresh air mass flow rate greater than said mass flow rate surge value, as a function of said speed signal;
 and wherein said control computer is configured to determine said flow ratio further as a function of said mass flow rate surge limit. 
 
   
   
     12. The system of  claim 11  wherein said control computer is configured to determine a surge limit percentage as a sum of one and a ratio of said mass flow rate surge limit and one hundred;
 and wherein said control computer is configured to compute a mass flow rate limit as a product of said mass flow rate surge value and said surge limit percentage, and to determine said flow ratio as a ratio of said mass flow rate limit and of said mass flow of fresh air. 
 
   
   
     13. The system of  claim 1  wherein said mass flow rate parameter is a charge flow value corresponding to a mass flow rate of a combination of fresh air supplied to said intake manifold via said compressor and recirculated exhaust gas supplied to said intake manifold via said EGR valve;
 and wherein said control computer is configured to limit said EGR valve control signal as a function of said mass flow rate surge value and said charge flow value. 
 
   
   
     14. The system of  claim 13  wherein said control computer includes:
 means for producing an EGR fraction command corresponding to a desired fraction of recirculated exhaust gas relative to an air charge supplied to said intake manifold, said air charge being said combination of fresh air and recirculated exhaust gas; 
 means for determining a maximum EGR fraction value as a function of said mass flow rate surge value and said charge flow value, said maximum EGR fraction value corresponding to an EGR fraction below which said turbocharger compressor surge s avoided; 
 means for producing a limited EGR fraction command as a function of said EGR fraction command and said maximum EGR fraction value; and 
 means responsive to said limited EGR fraction command to produce said EGR valve control signal. 
 
   
   
     15. The system of  claim 14  wherein said means for determining a maximum EGR fraction value includes:
 means for computing a maximum EGR flow rate value as said charge flow value less said mass flow rate surge value; and 
 means for computing said maximum EGR fraction value as a function of said maximum EGR flow rate value. 
 
   
   
     16. The system of  claim 14  wherein said control computer is further configured to determine a mass flow rate surge limit, corresponding to a fresh air mass flow rate greater than said mass flow rate surge value, as a function of said speed signal;
 and wherein said control computer is configured to determine said flow ratio further as a function of said mass flow rate surge limit. 
 
   
   
     17. The system of  claim 16  wherein said control computer is configured to determine a surge limit percentage as a sum of one and a ratio of said mass flow rate surge limit and one hundred;
 and wherein said control computer is configured to compute a mass flow rate limit as a product of said mass flow rate surge value and said surge limit percentage, and to determine said flow ratio as a ratio of said mass flow rate limit and of said mass flow of fresh air. 
 
   
   
     18. The system of  claim 13  wherein said control computer includes:
 means for determining a reduction value as a function of said mass flow rate surge value and said charge flow value, said reduction value corresponding to an amount of reduction of said exhaust gas flow through said EGR valve required to maintain exhaust gas flow therethrough at said flow rate below which said turbocharger compressor surge is avoided; and 
 means for limiting said EGR valve control signal as a function of said reduction value and of said EGR valve control signal. 
 
   
   
     19. The system of  claim 18  wherein said control computer is further configured to determine a mass flow rate surge limit, corresponding to a fresh air mass flow rate greater than said mass flow rate surge value, as a function of said speed signal;
 and wherein said control computer is configured to determine said flow ratio further as a function of said mass flow rate surge limit. 
 
   
   
     20. The system of  claim 19  wherein said control computer is configured to determine a surge limit percentage as a sum of one and a ratio of said mass flow rate surge limit and one hundred;
 and wherein said control computer is configured to compute a mass flow rate limit as a product of said mass flow rate surge value and said surge limit percentage, and to determine said flow ratio as a ratio of said mass flow rate limit and of said mass flow of fresh air.